1. Field
This application relates to communication networks and, more particularly, to a method and apparatus for enabling multicast transmissions to occur over a split multilink trunk.
2. Description of the Related Art
Data communication networks may include various computers, servers, hubs, switches, nodes, routers, proxies, and other devices coupled to and configured to pass data to one another. These devices will be referred to herein as “network elements”. Data is communicated through the data communication network by passing protocol data units, such as frames, packets, cells, or segments, between the network elements by utilizing one or more communication links. A particular protocol data unit may be handled by multiple network elements and cross multiple communication links as it travels between its source and its destination over the network.
FIG. 1 illustrates one example of a communication network 10. As illustrated in FIG. 1, subscribers 12 access the network 10 by interfacing with one or more Provider Edge (PE) network elements 14. The provider edge network elements collect traffic from multiple subscribers and multiplex the traffic onto the network backbone, which includes multiple Provider (P) network elements 16 connected together. The subscribers 12 thus may obtain access to the network 10 to exchange data with other subscribers, to obtain access to networked resources, or otherwise to take advantage of the communication services provided by the communication network.
One way to make networks more reliable is to provide redundant connections at the network level. For example, a connection at the edge of the network between a subscriber and PE network element, or between PE and P network elements may be created from multiple links that are configured to interconnect one or more subscriber gateways to one or more provider edges. To facilitate management, although physically the links are separate, logically they may be viewed as a single trunk so that a failure of one of the links forming the trunk will not require the network element to take any corrective action. Rather, the network is able to accommodate the failure by causing traffic to be shifted to the other link(s) forming the multi-link trunk. One example of multilink trunking is provided in U.S. patent application Ser. No. 10/125,654, filed Apr. 19, 2002, entitled System, Device, and Method For Improving Communication Using Trunk Splitting, the content of which is hereby incorporated herein by reference. Similarly, a way of implementing routing on a split multilink trunking system is provided in U.S. patent Ser. No. 10/618,136, filed Jul. 11, 2003, entitled Routed Split Multilink Trunking, the content of which is hereby incorporated by reference.
Traffic on a communication network may be classified according to how it is addressed. For example, broadcast traffic is addressed to all recipients, unicast traffic is addressed to a particular recipient, and multicast traffic is addressed to a plurality of recipients. Depending on the particular application and type of traffic, it may make sense to multicast the traffic rather than unicasting the traffic to multiple recipients.
Many multicasting protocols have been developed to allow traffic to be multicast on a communication network. Two such multicast protocols that have gained some acceptance in the networking industry include Protocol Independent Multicast (PIM) and Distance Vector Multicast Routing Protocol (DVMRP), although other protocols are also being discussed and implemented. Since multicast transmissions are expected to increase as networks continue to develop, it would be advantageous to allow multicast protocols to operate in a split multilink trunking environment. Additionally, it would be advantageous to enable sub-second recovery to occur upon failure, to provide layer 3 protocols at the edge of the SMLT, and to provide support for square SMLT.